Replace mitchellh dependencies with hashicorp

[BenV]

I had to do this in order to get go build to work properly. This is my first time ever playing with Go, so feel free to just reject this if I'm way off base. Thanks!

[dijit]

Didn't build until I pulled this change.

Probably a good idea to merge.

[saily]

Have a similar need and would love to give this a try. @dwickern could we get this merged?

[dwickern]

I can merge this but I'm afraid it will need more work.

This project is built with goxc which is now archived, and it's published to bintray which has shut down. It would need to be changed to build with GitHub Actions and deploy to GitHub Releases.

Packer plugins are structured differently now. Packer expects a repository named packer-plugin-X containing a directory for each postprocessor, builder, provisioner, etc. See the upgrade guide, scaffolding repo and an example post-processor.

I will archive this repo. Feel free to use the code to develop your own packer plugin. Or maybe they would accept this postprocessor functionality in https://github.com/hashicorp/packer-plugin-hyperv.